From the old media and films, Americans definitely sounded different from today- up to late 1950s thereabout. President Eisenhower then still sounded like Humphrey Bogart before- that flat flowing self assured even smooth dribbling assured flowing flat assured dribbling style. But right thenabout you start to hear more of today's accent, and no later than mid 1960s there was no more Bogart. And even people who at one time or another sounded that way- Lauren Bacall, Katharine Hepburn- when you hear them thereafter it is today's accent, or rather, style.
Accent or style, a most interesting cultural evolution. Y'all's insights please ?
Since I have come to know phonology, though not necessarily with the technical name, I've always been interested in it and have paid close attention to English and Persian phonology and accents. Yes, accents are most curious and interesting. I always consider the tribes that first settles here in Iran. Taking one of them, its people would pronounce a word as 'taraaneh'. Then at one point in time, a group of that tribe migrated to some other part of the country. And then at one time they started to pronounce the same word 'teraanah'. What on earth made them tick? I wonder!!
I can imagine that it didn't actually 'start' at one point, but that it was a process. But I find no reason for that.
Perhaps the change in phonology occurred as a result of the burgeoning of television, which began in the 50s and which became ubiquitous by the late 60s--even in the homes of the stars. In the preceding decades, when radio dominated the delivery of home consumed entertainment, news, and political rhetoric, a flat, smooth, self-assured tone was most effective at conveying coolness, strength, and wisdom--characteristics people found most appealing in their political leaders and in the protagonists of radio dramas, especially during the tumultuous first half of the 20th century. There was also a strong element of regionalism in the "old style" of speaking, with the bulk of entertainment and nationally known politicians hailing from New England, New York and the Atlantic seaboard.
When television took over from radio and movies, a more subtle, emotionally nuanced, one might say less robotic, delivery evolved. Performers, politicians and subsequently the population in general tuned their instruments to a naturalistic style that better fit the intimate new medium--the wooden, flat tones of the past had to yield to a style that sounded, and looked, more human and real. This coincided with the warming sensitivities coming to the fore in civic discourse, the arts, and society in general as the 60s progressed. Additionally, the domination of the east coast "style" was thenabout challenged and diluted by the rise of the west coast media industry and the influx there of talent from a much broader cross section of the American melting pot. The modern style has continued to self-reinforce as the hours and hours of time spent producing and consuming television has mounted and mounted.
Your explanations make sense. I must add that this is much more a matter of speaking style than accent, if accent at all.
Your point about the influence of New England fits well with that English actors (notably David Niven, Laurence Olivier, Charles Lawton) speak with quite a different style, I might say more casual and realistic than the 'Bogart' style, even while acting in American films.
But that raises doubt about the influence of the radio, because so far as my observations above, the radio apparently didn’t have a similar effect on Britons. Even on the American side, I doubt that the Marx Brothers, whose acts are a bit more than just voices, care to take cue from radio at all. ( Unless they might have had all along for comedic effects, an element of their acts that I for one have failed to notice all these years-- the complete and absurd incongruity between their acrobatic slapsticks and their flat machine gun voices. Anyway, there is no lack of other famous people to have doubt about.)
Television? I definitely buy that it being such a cultural juggernaut must have contributed to making our modern speech what it is. But has that been only a return to some 'pre-Bogart' time, or an evolution to a new speaking style entirely, so that we now speak like no other generations before, and are helpless about what Lincoln or Washington sounded like, or for that matter Shakespeare ?